The present invention is directed to a pulley and belt combination and a drive system incorporating the pulley and belt.
Pulley and belt combinations are well known and there are many different types of belts and many different combinations of belts and pulleys. The belt application typically determines the belt construction, while the belt construction is a factor in the pulley construction. If the inner face of the belt is comprised of teeth, then the outer face of the drive pulley, which contacts the inner face of the belt, is conventionally formed with grooves corresponding to the tooth profile of the belt. For synchronous drive belts wherein the teeth extend laterally across the width of the belt, the corresponding pulleys are provided with flanges to prevent the belt from travelling off of the pulley. For drive belts with self-tracking tooth profiles, i.e. a profile that results in the belt automatically tracking to one position on the correspondingly grooved pulley, the pulleys do not require flanges to restrain the axial movement of the belt. If the inner face of the belt is toothless, then the outer face of the pulley is correspondingly grooveless.
A simplistic description of a timing belt system is that the system consists of a toothed timing belt, a driver pulley which is powered to drive the timing belt, and a driven pulley about which the timing belt travels. To reduce tooth abrasion of the belt, and improve belt wear and belt life, the coefficient of friction between the belt and pulley is reduced as much as possible. A low coefficient of friction does not alter the performance of the drive system, as the belt is driven, not by friction, but by the positive engagement between the timing belt and pulley teeth. Conventionally, the surface material of the driven pulley, the non-powered pulley, is also selected for a low coefficient of friction between the belt and the pulley, and again, the belt is driven by the engagement between the belt and pulley teeth. In such a timing belt system, it is easy to achieve the desired coefficients of friction between the timing belt and both of the pulleys since the entire system is predominantly driven by the positive engagement of the mating surfaces of the belt and pulleys.
However, to achieve the goals of reduced space and minimized noise in a drive system, the present invention utilizes both a toothed driver pulley and a flat toothless driven pulley with a timing belt. It is known to drive a synchronous drive belt on a driven pulley that has no corresponding grooves. However, to maintain the belt on the pulley, the pulley is provided with either flanges to restrain the lateral edges of the belt or the pulley is provided with a crowned surface to encourage the belt to travel along the central portion of the pulley (see U.S. Pat. Nos. 4,979,928 and 4,589,861). A combination of flanges and a crowned pulley surface may also be used to restrain the belt as it travels about the pulley. Additionally, because of the reduced contact between the toothed belt surface and the grooveless pulley surface, the belt and pulley combination is provided with enough wrap to enable the drive pulley to properly drive the belt. Another way to achieve the proper torque in the drive system is to modify the belt surface for an increased coefficient of friction. However, in the present invention the belt surface must be formed from a material that provides a low coefficient of friction with the driver pulley surface; creating conflicting requirements for the construction of the belt.
GB 2158180 discloses a belt drive arrangement wherein pulleys are driven off both the front and the back of a toothed belt. The belt contact surface of the back driven pulley is provided with a rubber material to produce a high coefficient of friction between the pulley surface and the material of the toothless back of the belt. However, the inside surface of the belt is provided with teeth to provide a positive engagement with a corresponding grooved drive pulley.
The present invention is directed toward a drive system comprising a drive belt, a driven pulley, and a driver pulley wherein the combination is modified to minimize noise when in operation.
The belt has a pulley engaging surface which contacts both the surface of the driver pulley and contacts the belt engaging surface of the driven pulley. The driven pulley has a non-grooved, crownless belt engaging surface.
In an aspect of the invention, the material forming the pulley engaging surface of the belt has a relatively low coefficient of friction, and the material forming the belt engaging surface of the driven pulley has a relatively high coefficient of friction.
In another aspect of the invention, the material forming the pulley engaging surface of the belt has a coefficient of friction of not more than 0.45.
In another aspect of the invention, the material forming the belt engaging surface of the driven pulley has a coefficient of friction of 0.45 or greater.